X-ray systems are used for medical, industrial and security inspection purposes because they can cost-effectively generate images of internal spaces not visible to the human eye. Materials exposed to X-ray radiation absorb differing amounts of X-ray radiation and, therefore, attenuate an X-ray beam to varying degrees, resulting in a transmitted or backscattered level of radiation that is characteristic of the material. The attenuated or backscattered radiation can be used to generate a useful depiction of the contents of the irradiated object. A typical single energy X-ray configuration used in security inspection equipment may have a fan-shaped or scanning X-ray beam that is transmitted through or backscattered by the object inspected. The absorption or backscattering of X-rays is measured by detectors after the beam has passed through the object and an image is produced of its contents and presented to an operator.
Trade fraud, smuggling and terrorism have increased the need for such non-intrusive inspection systems in applications ranging from curbside inspection of parked vehicles to scanning in congested or high-traffic ports because transportation systems, which efficiently provide for the movement of commodities across borders, also provide opportunities for the inclusion of contraband items such as weapons, explosives, illicit drugs and precious metals. The term port, while generally accepted as referring to a seaport, also applies to a land border crossing or any port of entry.
With an increase in global commerce, port authorities require additional sea berths and associated container storage space. Additional space requirements are typically met by the introduction of higher container stacks, an expansion of ports along the coastline or by moving inland. However, these scenarios are not typically feasible. Space is generally in substantial demand and short supply. Existing ports operate under a routine that is not easily modified without causing disruption to the entire infrastructure of the port. The introduction of new procedures or technologies often requires a substantial change in existing port operating procedures in order to contribute to the port's throughput, efficiency and operability.
With limited space and a need to expand, finding suitable space to accommodate additional inspection facilities along the normal process route remains difficult. Additionally, selected locations are not necessarily permanent enough for port operators to commit to the long term installation of inspection equipment. Moreover, systems incorporating high-energy X-ray sources, or linear accelerators (LINAC), require either a major investment in shielding material (generally in the form of concrete formations or buildings) or the use of exclusion zones (dead space) around the building itself. In either case, the building footprint is significant depending upon the size of cargo containers to be inspected.
A mobile inspection system offers an appropriate solution to the need for flexible, enhanced inspection capabilities. Because the system is relocatable and investing in a permanent building in which to accommodate the equipment is obviated, site allocation becomes less of an issue and introducing such a system becomes less disruptive. Also, a mobile X-ray system provides operators, via higher throughput, with the ability to inspect a larger array of cargo, shipments, vehicles, and other containers.
Conventional relocatable inspection systems generally comprise at least two booms, wherein one boom will contain a plurality of detectors and the other boom will contain at least one X-ray source. The detectors and X-ray source work in unison to scan the cargo on the moving vehicle. In conventional single boom relocatable inspection systems, the X-ray source is located on a truck or flatbed and the detectors on a boom structure extending outward from the truck. These systems are characterized by moving-scan-engine systems wherein the source-detector system moves with respect to a stationary object to be inspected. Also, the detectors and the source of radiation are either mounted on a moveable bed, boom or a vehicle such that they are integrally bound with the vehicle. This limits the flexibility of dismantling the entire system for optimum portability and adjustable deployment to accommodate a wide array of different sized cargo, shipments, vehicles, and other containers. As a result these systems can be complicated to deploy and pose several disadvantages and constraints. Conventional systems are disadvantageous in that they suffer from a lack of rigidity, are difficult to implement, and/or have smaller fields of vision.
Accordingly, there is need for improved inspection methods and systems built into a fully self-contained, over-the-road-legal vehicle that can be brought to a site and rapidly deployed for inspection. The improved method and system can, therefore, service multiple inspection sites and set up surprise inspections to thwart contraband traffickers who typically divert smuggling operations from border crossings that have tough interdiction measures to softer crossings with lesser inspection capabilities. Moreover, there is an additional need for methods and systems that require minimal footprint to perform inspection and that use a sufficient range of radiation energy spectrum to encompass safe and effective scanning of light commercial vehicles as well as substantially loaded 20-foot or 40-foot ISO cargo containers. It is important that such scanning is performed without comprising the integrity of the cargo and should ideally be readily deployable in a variety of environments ranging from airports to ports of entry where a single-sided inspection mode needs to be used due to congested environments. Similar needs are addressed in U.S. Pat. No. 6,543,599, entitled “Self-Contained Portable Inspection System and Method”, which is herein incorporated by reference in its entirety. In addition, there is a need for improved methods and systems that can provide comprehensive cargo scanning in portable and stationary settings.
Further, in the mobile cargo inspection systems known in the art, the boom structures are typically heavy, thereby causing the overall weight of the scanning system to be close to, or even over the allowable axle load limits. Further, the booms are bulky when stowed such that the vehicle is approximately 4 m high above road level. This makes a mobile scanning system not only difficult to manoeuvre but also restricts its movement in different territories due to the applicable road restrictions on carriage weight. Therefore, there is also a need for a scanning system that can be stowed in a relatively compact area so that it can be easily transported on road, as well as by air. In addition, there is also a need for a scanning system which is light weight, and has a low height and center of gravity in a stowed position, thereby allowing for road transport even in challenging, steep and hilly areas.
Further, inspection typically occurs from only three or fewer directions. For example, a transmission X-ray system will be deployed in a side-shooter or top-shooter configuration while a backscatter system is generally only available in single-sided or three-sided configurations.
Therefore, what is also needed is a four-sided imaging system which provides high detection performance using a combination of transmission and backscatter imaging sensors.